It is often desired to generate multiple spot beams in commercial communication satellites. Multiple spot beams can be generated by using a multi-element antenna and beamforming the signals received or transmitted by the antenna.
By using digital beamforming techniques and applying complex digital weights to the antenna element signals for each communication frequency channel, a large number of narrow spot beams can be achieved. However, digital beamformers have a limited dynamic range. A typical dynamic range for a digital beamformer is around 50 dB. Because of the limited dynamic range, digital beamformers can be vulnerable to high power interfering signals when operating in receive mode. The dynamic range can be increased but at high costs. Moreover, a sufficiently strong interfering signal, directed at the communication satellite, can render the digital beamformer inoperative. Interfering signals with a high power can also saturate other digital signal processing components of the antenna.
It is known to partition elements of a multi-element antenna into a number of subarrays in order to reduce the number of beamforming control points in the digital beamforming network and thereby simplify the beamforming network.
The invention was made in this context.